To meet the demand for wireless data traffic having increased since deployment of 4th generation (4G) communication systems, efforts have been made to develop an improved 5th generation (5G) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post long term evolution (LTE) System’. The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), full dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems. In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, coordinated multi-points (CoMP), reception-end interference cancellation and the like. In the 5G system, hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM) (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.
The internet, which is a human centered connectivity network where humans generate and consume information, is now evolving to the internet of things (IoT) where distributed entities, such as things, exchange and process information without human intervention. The internet of everything (IoE), which is a combination of the IoT technology and the big data processing technology through connection with a cloud server, has emerged. As technology elements, such as “sensing technology”, “wired/wireless communication and network infrastructure”, “service interface technology”, and “security technology” have been demanded for IoT implementation, a sensor network, a machine-to-machine (M2M) communication, machine type communication (MTC), and so forth have been recently researched. Such an IoT environment may provide intelligent Internet technology services that create a new value to human life by collecting and analyzing data generated among connected things. IoT may be applied to a variety of fields including smart home, smart building, smart city, smart car or connected cars, smart grid, health care, smart appliances and advanced medical services through convergence and combination between existing information technology (IT) and various industrial applications.
In line with this, various attempts have been made to apply 5G communication systems to IoT networks. For example, technologies, such as a sensor network, MTC, and M2M communication may be implemented by beamforming, MIMO, and array antennas. Application of a cloud RAN as the above-described big data processing technology may also be considered to be as an example of convergence between the 5G technology and the IoT technology.
MIMO systems may be classified into a closed-loop MIMO system and an open-loop MIMO system, depending on whether precoding matrix indicator (PMI) information on a receiver is used in forming a transmission beam pattern.
In case of the closed-loop MIMO system, an evolved node B (eNB) that receives a PMI feedback from a user equipment (UE) is specified to communicate with the UE by using appropriate transmission/reception precoding, based on received information. Contrary to the closed-loop MIMO system, in case of the open-loop MIMO system, a receiver does not deliver PMI information to a transmitter. Instead, the receiver of the open-loop MIMO system finds a supportable transmission rate by assuming precoding defined in advance by the method specified in the standard or higher signaling, as precoding to be assumed as to a time and frequency space when generating channel quality indicator (CQI) according to time and frequency resources, and delivers this to the transmitter through the CQI.
In general, it is known that the closed-loop MIMO may adaptively utilize channel information and thus has greater system performance in comparison with the open-loop MIMO. The reason is that while the closed-loop MIMO has a process of selecting the precoding preferred by the UE and notifying it to the eNB, the open-loop MIMO has no such process and thereby has difficulty in applying the precoding preferred by the UE whenever the eNB transmits a signal to the UE.
However, transmission/reception of signals through the closed-loop MIMO requires an additional overhead, such as transmission of PMI from the UE to the eNB. In addition, in a situation where a moving speed of a UE is very fast or a channel is suddenly changed, a beam pattern of an interference signal changes rapidly with time, and a performance loss due to a change of the interference signal may occur. On the other hand, the open-loop MIMO system has some advantages, such as small effects of dynamic interference and small feedback overhead for PMI even though the performance efficiency of the system itself is lower than that of the closed-loop MIMO system. A semi closed-loop MIMO may be considered to exploit the advantages of and to compensate the disadvantages of the open-loop MIMO and the closed-loop MIMO. In the semi closed-loop MIMO, the UE reports, to the eNB, part of PMI information other than the entire PMI information, and the eNB circulates a non-reported PMI part in the corresponding part of PMI information and transmits data to the UE.
Meanwhile, in the closed-loop MIMO or the semi closed-loop MIMO in which the UE provides feedback information to the eNB, the amount of feedback information to be transmitted on limited resources increases because of carrier aggregation (CA) or the like, thus resulting in a signal overhead issue.
Therefore, a need exists for a method and an apparatus for reporting a channel status by using a channel status information reference signal (CSI-RS) in a mobile communication system.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.